1. Field of the Invention
The present invention relates to a process for producing ring-opened polymers from monomers of a norbornene type which are defined later (hereinafter these monomers are referred to as norbornene-type monomers or norbornene derivatives). More particularly, the invention relates to ring-opened norbornene derivative polymers which have narrow molecular weight distributions, contain no gel, and are best suited as materials for optical purposes and (ii) a process for producing said polymers.
2. Description of the Prior Art
Polymethyl methacrylate and polycarbonate have been used up to now as macromolecular materials for optical purposes. However, polymethyl methacrylate has a strong tendency to absorb water or moisture and polycarbonate involves the problem that birefringence tends to occur in molded articles of this polymer because it has basically benzene rings and generally high melt viscosity. Hence it is becoming difficult for these polymers to meet performance requirements that are becoming increasingly sophisticated.
In recent years, polymers from norbornene-type polycyclic monomers have been developed as macromolecular materials substantially free of the above noted drawbacks.
For example, Japanese Patent Application Kokai No. Sho. 60-26024 describes that a product of hydrogenating a polymer obtained by the ring-opening polymerization of a tetracyclododecene compound alone or a monomer mixture of the compound and a norbornene compound is superior in transparency, water resistance, and heat resistance and Japanese Patent Application Kokai Nos. Sho. 60-168708 and Sho. 61-292601 disclose that addition copolymers of .alpha.-olefins with a tetracyclododecene compound or with a norbornene-type monomer having five or more rings are superior in transparency, heat resistance, chemical resistance, and water resistance. As set forth in these patent applications, polymers from norbornene-type polycyclic monomers have better properties as macromolecular compounds for optical applications.
Meanwhile, alkylidene-containing norbornene-type monomers represented by the following formula [I] are readily obtainable by Diels-Alder reaction of cyclopentadiene with allene or a linear conjugated diene, followed by displacement of a double bond. ##STR2##
In this formula, R.sub.1 and R.sub.2 are the same or different and each denote hydrogen or alkyl and m denotes an integer of 0 to 2.
In particular, ethylidene-containing monomers of formula [I] are far more readily available than the other norbornene-type monomers since ethylidene-norbornene is manufactured in large quantities as a comonomer for its ethylene-propylene terpolymer.
Considering the structure of polymers produced by the ring-opening polymerization of norbornene-type monomers represented by the above formula [I], it is expected that these polymers will be superior in optical properties including transparency and the hydrogenation of these polymers provide polymers more fitted for optical applications. However, no process comprising the ring-opening polymerization of this type of monomer has been known up to now that can yield a polymer which is neither cross-linked nor in gel form and has properties of utility for optical purposes.
It is already known that polymers are producible from norbornene-type monomers of formula [I] by ring-opening bulk polymerization in molds in the presence of a methathesis catalyst. For example, Japanese Patent Application Kokai No. Sho. 63-97611 describes the reaction injection molding (RIM) method to polymerize 5-thylidene-2-norbornene in a mold in the presence of a methathesis catalyst and Japanese Patent Application Kokai No. Sho. 63-37108 (corresponding to EP 251,033) describes the RIM method of polymerizing 6-alkylidene-2-tetracylododecene.
However, all of these polymers obtained by the RIM method are cross-linked and unsuited for optical purposes. The above J. P. Appln. Kokai No. Sho. 63-37108 suggests that a linear polymer of 6-alkylidene-2-tetracyclododecene will be producible by the methathesis polymerization under mild conditions such as those of solution polymerization, but this patent application points out that such a linear polymer, if obtained, will have poor moldability and processability and hence will be unsuitable for practical use.
While Example 11 in this patent application illustrates an experiment of solution-polymerizing ethylidene-tetracylododecene in the presence of a diethylaluminum chloride/tungsten hexahalide catalyst system, the product was reportedly a substance in gel form (that is, the reaction product mixture was not homogeneous), in spite of a 10% or less dilute monomer solution used in the polymerization. In this patent application, an IR spectrum of the product this obtained is shown and it is set forth on the basis of the spectrum that the product is a ring-opened polymer. In this spectrum, however, an absorption between 950 and 1000 cm.sup.-1, which indicates the presence of double bonds in the main chain (see Makromol. Chem., 78, 231 (1964)), is weak and on the other hand a strong absorption of ambiguous assignment is observed in the vicinity of 1700 cm.sup.-1. Such a spectrum cannot clarify whether the product is a ring-opened polymer.
The present inventors polymerized the above monomer by using a conventional ring-opening polymerization catalyst system combining an organoaluminum compound with each of transition metal compounds (a tungsten compound and a molybdenum compound), with the result that none of the polymers could be obtained but those, in gel form or having broad molecular weight distributions, which were unfitted for optical applications.
Solution polymerization of 5-methylidenenorbornene, which is one of the monomers represented by the above formula [I], is also known, but no ring-opened polymer can be obtained in this case unless a special methathesis catalyst is used. For example, it is reported that no solvent-soluble polymer is formed with a triethylaluminum/titanium tetrachloride catalyst system (Makromol. Chem., Rapid Commun, 1, 467-472 (1980)).